1. Field of the Invention
The present invention relates to an eddy current deceleration device that applies deceleration braking to a vehicle.
2. Description of the Related Art
The present inventor has previously developed an eddy current deceleration device as shown in FIG. 34 to FIG. 36. As shown in these Figures, this eddy current deceleration device a comprises a drum-shaped rotor c that is mounted on a power transmission system such as a drive shaft b of a vehicle and a stator d (source of magnetic force) mounted on a fixed system such as a vehicle transmission. The vehicle is decelerated and braked by generating eddy currents in the rotor c by supplying magnetism from the stator d to the rotor c. The deceleration braking is released by shielding the magnetism within the stator d.
The stator d comprises a hollow ring-shaped casing e that is supported on a fixed system, a magnetic ring g that is freely rotatably accommodated, by means of a bush f, in the interior of the casing e and an actuator (cylinder h or the like) that rotates the magnetic ring g. As shown in FIG. 35 and FIG. 36, the magnetic ring g comprises a support ring i made of a non-magnetic body, a plurality of permanent magnets j mounted with a prescribed spacing in the circumferential direction on the support ring i and magnetic members k interposed between each of the permanent magnets j. These permanent magnets j have magnetic pole faces at the respective opposite end faces in the circumferential direction and are arranged such that facing poles thereof in the circumferential direction are of the same polarity. In addition, on the casing e, there are alternately arranged along the circumferential direction pole pieces 1 made of magnetic material (soft magnetic material) positioned in a region between the magnetic ring g and the rotor c and supports m made of non-magnetic material that support these pole pieces. As shown in FIG. 36, the circumferential length of the pole pieces 1 matches the circumferential length of the magnetic members k.
With this construction, as shown in FIG. 35, when the permanent magnets j are positioned below the pole pieces 1 by rotating the magnetic ring g with the cylinder h, the magnetism of the permanent magnets j is shielded by the pole pieces 1, constituting a short-circuit n, so no eddy current is generated in the rotor c and no deceleration braking is produced in the vehicle. In contrast, as shown in FIG. 36, when the magnetic members k are positioned below the pole pieces 1, a magnetic circuit o linking the N pole and S pole is constituted between the permanent magnet j and the rotor c, so eddy current is generated in the rotor c, producing deceleration braking of the vehicle.
In order to increase the braking force in such an eddy current deceleration device a, it is important to intensify the magnetic force of the permanent magnets j of the magnetic ring g. However, as shown in FIG. 35 and FIG. 36, if the permanent magnets j are arranged with facing magnetic poles in the circumferential direction thereof being of the same polarity, when the permanent magnets j are magnetized after assembly of the permanent magnets j and magnetic members k in ring fashion, sufficient magnetization of the permanent magnets j cannot be achieved unless the circumferential length of the pole pieces k interposed between these permanent magnets j is expanded to a certain extent. Consequently, if magnetization of the permanent magnets j is prioritized, the gaps between the permanent magnets j have to be widened to a certain extent, thereby restricting the number of permanent magnets j that can be provided. On the other hand, if the number of permanent magnets j that are to be provided is prioritized, magnetization becomes insufficient because the gap therebetween is reduced. It was therefore difficult to increase the braking force.
Also, as shown in FIG. 35, although, when the deceleration braking is turned off, a dominant part of the magnetism of the permanent magnets j is shielded within the casing e by the pole pieces 1, some portion thereof leaks to the rotor c through the supports m made of non-magnetic material, thereby constituting a magnetic leakage circuit p. Weak eddy currents are thereby generated in the rotor c, giving rise to dragging braking, which has an adverse effect on fuel consumption of the vehicle.
Related prior art is disclosed in for example Japanese Patent Publication Nos. H. 6-83570, H. 6-83571, and H. 7-118901, and Japanese Laid-open Patent Application Nos. 2000-350432 and 2001-8436.
An object of the present invention, which was created in view of the above, is to provide an eddy current deceleration device wherein braking force can be increased and dragging braking prevented.